This invention relates generally to hermetic, sealed refrigeration compressors, and more particularly to an oil pumping system for lubricating the internal moving parts of such a compressor.
Hermetic refrigeration compressors have a sealed metal casing to which are directly connected the refrigerant outlet and return lines and the pumping mechanism must be located completely within the sealed casing. A conventional construction for such a compressor consists of a motor and reciprocating piston-type pump mounted as a unit on springs within the casing and generally arranged so that the motor is connected directly to the crankshaft for reciprocating the piston and arranged in a vertical orientation with the motor portion at the bottom and the cylinder housing containing the piston at the upper end. The bottom of the casing is filled with a quantity of lubricating oil and a pumping arrangement is used generally including internal passages in the crankshaft for forcing that oil upward to lubricate the various bearings and the crankpin and connecting rod to give a positive flow of oil under all conditions.
Normally, such compressors use two-pole motors, and therefore run at a relatively high speed of a nominal 3600 r.p.m. At this speed, it is possible to rely on centrifugal force within the crankshaft to provide the pumping action to force the oil upwards through the internal passages in the crankshaft and outward to the various bearings requiring lubrication. This centrifugal force can be employed in a number of ways, and may merely use a vertical eccentric passage in the crankshaft whose lower end is immersed below the upper surface of the oil. As the crankshaft rotates, the fact that the passage is eccentric exerts a force on the oil, tending to create a pressure within the passage which results in upward movement of the oil.
A problem arises, however, when compressors are operated at a lower speed, such as when they are driven by a four-pole motor where the nominal speed is therefore only 1800 r.p.m. In such cases, the centrifugal force may not be sufficient to maintain an adequate flow of oil to the uppermost bearings and various arrangements have been employed to augment the oil flow in addition to the pumping action provided by centrifugal force. One such example is shown in U.S. Pat. No. 3,182,901, where the crankshaft has a horizontal slot at the bottom designed to allow centrifugal force to force the oil radially outward with respect to the axis of the crankshaft to the crankshaft external surface. A helical passage is then provided around the outside of the crankshaft and the oil passes up this helical passage to another opening where it passes inside the crankshaft to a vertical, offset passage which conducts the oil to the upper parts of the compressor. Thus, the centrifugal force is augmented by the lifting force of the helical screw threadlike passage to increase the oil flow above what would have been available merely from centrifugal force. However, such constructions require relatively expensive machining of the helical passage and the amount of assistance provided by the helical passage can vary considerably, depending upon the temperature at which the compressor is operating, and hence the viscosity of the oil.